1. Field of the Invention
This invention relates to monitoring the vibration of a turbine shaft in an operating turbine and more particularly to detecting and measuring angular shaft vibration, torque and power.
2. Description of the Prior Art
Shaft torque can be measured by using strain gages affixed to the shaft and obtaining their output by means of slip rings or telemetry. Non-contacting measurement of shaft torque and shaft vibration can be made by using fixed probes and detecting a keyway or reflective tape segment passing the fixed probes. For torque, two such probes separated by a known shaft length and shaft cross section are required. But when linear shaft position changes occur, or when linear vibration occurs, significant errors can result in both the angular vibration measurement and the torque measurement. This is because early arrival of the keyway or tape segment at the fixed probe could be caused by linear or angular motions.